The blank ursaGrid object is generated by calling of ursa_grid() without arguments. These approaches provide unified sequence of list's items:
List of 9
$ columns: int NA
$ rows : int NA
$ resx : num NA
$ resy : num NA
$ minx : num NA
$ maxx : num NA
$ miny : num NA
$ maxy : num NA
$ proj4 : chr ""
- attr(*, "class")= chr "ursaGrid"
NULL